1. Field of the Invention
The present invention relates to a process for producing a carboxyl group-containing vinylidene fluoride copolymer and more particularly to a process for producing a carboxyl group-containing vinylidene fluoride copolymer for effective used as an oligomer having a functional group at both terminals.
2. Description of Related Art
Functional oligomers having a carboxyl group at both terminals can be effectively used as a chain-elongating agent for epoxy resin, isocyanate resin, etc., or as raw materials for a solvent-resistant sealant, an adhesive, a coating agent, etc., but carboxyl group-containing fluorine-based copolymers cannot be safely produced at a low cost according to the conventional processes as mentioned below.
U.S. Pat. No. 3,147,314 discloses a process, which comprises boiling a vinylidene fluoride-hexafluoropropene copolymer together with an amine in tetrahydrofuran for a long time, thereby effecting dehydrofluorination reaction, followed by oxidative decomposition of the resulting double bond by KMnO.sub.4, where not only the dehydrofluorinated copolymer must be once isolated and then subjected to oxidation reaction upon redissolution into acetone, but also the heavy metal Mn used in the oxidative decomposition reaction must be removed. That is, the resulting pollution control is a problem.
Literature "Functional fluorine-containing polymers" pages 11-12 (1982), published by Nikkan Kogyo Shinbun, Japan, discloses a process, which comprises copolymerizing tetrafluoroethylene with CF.sub.2.dbd.CFO(CF.sub.2).sub.4 COOCH.sub.3, followed by hydrolysis of side chain ester groups, where the ester group-containing monomer used in the copolymerization reaction is very expensive and thus is not suitable for industrial application, and also the hydrolysis reaction of the ester group does not fully proceed unless under alkaline conditions and thus is hardly applicable to the vinylidene fluoride-based copolymers.